There exists a significant amount of activity in the field of on-line handwriting recognition. The prior art current to 1990 is reviewed in "The State of the Art in On-Line Handwriting Recognition" by Charles C. Tappert et al, IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 12, No. 8, August, 1990.
Generally speaking, on-line handwriting analysis is currently employed for two distinct applications: identity verification and input of handwritten letters and numbers into a computer. These two applications have sharply contrasting operational requirements and goals. Handwriting analysis for identity verification senses features of handwriting which are distinct for each individual and thus can be used to unambiguously identify a given individual. In contrast, handwriting analysis for alphanumeric input to a computer seeks to minimize the effect of the very features which are important for identity verification and to concentrate on universal handwriting characteristics which can be associated with given symbols independently of the individual writer.
Currently existing and proposed systems providing handwriting analysis for alphanumeric input to a computer are generally geared towards recognition of how a symbol looks rather than how it is created. Accordingly, such systems employ digitizers or graphic tablets.
Signature verification systems, on the other hand, attempt to identify biometric characteristics of the writer and employ indications such as pressure and acceleration during writing.
U.S. Pat. No. 4,345,239 employs pen acceleration for use in a signature verification system. U.S. Pat. No. 5,054,088 employs both acceleration and pressure data characteristics of handwriting for identity verification. As indicated by the above patents, pen acceleration is employed for signature verification because it is a personal feature, characteristic of each individual. Accordingly, pen acceleration has not been employed for alpha-numeric input.
U.S. Pat. No. 4,751,741 describes pen-type character recognition apparatus which employs pen pressure data exclusively.
U.S. Pat. No. 4,695,741 describes a light-pen equipped with an accelerometer for detecting tapping of the pen on a computer screen. As indicated by the above patent, pen acceleration is not used more generally to determine contact between a pen and a surface.
U.S. Pat. No. 4,845,684 describes a hand-held ultrasonic apparatus for detecting contact between a pen and a writing surface. The above patent does not disclose use of acceleration data.
U.S. Pat. No. 4,122,435 describes an apparatus using accelerometers which, when employed to write on a special surface, produces signals which can be used for handwriting analysis.
Position digitization through ultrasonic position digitization is well-known in the prior art, as for example in U.S. Pat. Nos. 3,731,273; 4,317,005; 4,357,672; 4,578,674; 4,654,648; 4,758,691; 4,814,552; 4,862,152; 4,991,148; 5,142,506; 5,214,615; 5,239,139; and 5,280,457. Other publications describing ultrasonic position digitization include "A sonic pen: a digital stylus system" by Brenner and DeBruyne, IEEE Transactions on Computers, Vol. C-19, No. 6, June 1970, pp. 546-548; "Compact Large-Area Graphic Digitizer for PC" by DeBruyne, IEEE Computer Graphics and Applications, December 1986, pp. 49-53; IBM Technical Disclosure Bulletin, Vol. 12, No. 3., August 1969, p. 390; and "US Cursor Position Detection", IBM Technical Disclosure Bulletin, Vol. 27, No. 11, April 1985.
In practice digitized positions derived from ultrasonic measurement are not determined precisely enough to allow even minimally operative handwriting recognition, so that handwriting recognition from ultrasonic position detection is not known in the prior art.